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tools/sched_ext: scx_flatcg: fix potential stack overflow from VLA in fcg_read_stats

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fcg_read_stats() had a VLA allocating 21 * nr_cpus * 8 bytes on the
stack, risking stack overflow on large CPU counts (nr_cpus can be up
to 512).

Fix by using a single heap allocation with the correct size, reusing
it across all stat indices, and freeing it at the end.

Signed-off-by: David Carlier <devnexen@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
David Carlier 2026-02-14 07:32:05 +00:00 • committed by Tejun Heo
parent 0b82cc331d
commit cabd76bbc0
1 changed files with 9 additions and 4 deletions
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13
tools/sched_ext/scx_flatcg.c
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@ -102,22 +102,27 @@ static float read_cpu_util(__u64 *last_sum, __u64 *last_idle)
static void fcg_read_stats(struct scx_flatcg *skel, __u64 *stats)
{
__u64 cnts[FCG_NR_STATS][skel->rodata->nr_cpus];
__u64 *cnts;
__u32 idx;
cnts = calloc(skel->rodata->nr_cpus, sizeof(__u64));
if (!cnts)
return;
memset(stats, 0, sizeof(stats[0]) * FCG_NR_STATS);
memset(cnts, 0, sizeof(cnts));
for (idx = 0; idx < FCG_NR_STATS; idx++) {
int ret, cpu;
ret = bpf_map_lookup_elem(bpf_map__fd(skel->maps.stats),
&idx, cnts[idx]);
&idx, cnts);
if (ret < 0)
continue;
for (cpu = 0; cpu < skel->rodata->nr_cpus; cpu++)
stats[idx] += cnts[idx][cpu];
stats[idx] += cnts[cpu];
}
free(cnts);
}
int main(int argc, char **argv)